This invention relates to a surface emitting semiconductor laser/light emitting diode structure and, more particularly, to a high density surface emitting semiconductor structure with independently addressable individual light emitting elements.
The ability to fabricate closely spaced, or high density, independently addressable laser and light emitting diode (LED) sources is important for many applications such as optical disk technology, laser printing and scanning, optical interconnection and fiber optic communications.
Individually, semiconductor light emitting diodes and semiconductor lasers may have insufficient power for some of those applications. Arrays of semiconductor light emitting diodes or semiconductor lasers can be used to increase the power output, provide parallel processing, and to simplify optical system design. To provide and maintain good optical alignment of the light emitting elements of the array with one another and to minimize the assembly involved, arrays have been fabricated so that the light emitting elements are on a single semiconductor substrate.
One problem with such arrays is maintaining the electrical and optical isolation between the individual light emitting elements. Another problem is increasing the density of the light emitting elements in the substrate by closely spacing the elements together while still maintaining the isolation, avoiding heat dissipation problems, and providing precise alignment of the elements.
Another problem is making each individual light emitting element in the array independently addressable. As the light emitting elements are spaced closer together in higher densities, it is progressively more difficult to separately, individually and independently cause each element to emit light.
Typical laser and LED sources have been edge emitters. The light is emitted from the edge of a monolithic structure of semiconductor layers. An alternative construction is surface emitters where the light is emitted from the surface of the monolithic structure of semiconductor layers.
Surface emitting semiconductor light sources have several potential advantages over edge emitters. The light emitting surface of a surface emitter is larger than that of an edge emitter, therefore the power generated by a surface emitter is larger than that of an edge emitter. And the power needed to cause emission of light is less for a surface emitter than an edge emitter. Surface emitting LEDs are more efficient than edge emitting LEDs because of that larger emitting area. Fabrication of surface emitting lasers can be less complex than fabrication of edge emitting lasers since the cleaving and mirror passivation needed for edge emitters are eliminated.
It is an object of this invention, therefore, to provide a high density array of light source surface emitters on a single substrate.
It is a further object of this invention to provide a means for independent addressing of the individual laser or light emitting diode elements in this high density array.